In a Long Term Evolution (LTE) or Long Term Evolution Advanced (LTE-A) communications system, a downlink multiple access manner is usually an orthogonal frequency division multiple access (OFDMA) manner. A main characteristic of the orthogonal frequency division multiple access manner is that different user equipments use different time-frequency resources, to ensure that there is no interference with signal reception between the different user equipments, thereby implementing simple reception on a user equipment side. However, when communication is performed by using the orthogonal frequency division multiple access manner, utilization of the time-frequency resources is relatively low. Consequently, an overall transmission rate of the communications system is limited.
A transmission manner of non-orthogonal multiple access (NOMA) can be used to transmit information about a plurality of user equipments on a single resource unit. Compared with OFDMA, NOMA improves the overall transmission rate of the system. Further, in a transmission manner of semi-orthogonal multiple access (SOMA), a user equipment receiver is enabled, by using a characteristic of a Gray code in an existing modulation (or a constellation diagram) scheme, to use a simple receive algorithm, thereby further improving system performance. Some downlink transmission schemes including NOMA and SOMA are also collectively referred to as multi-user equipment superposition transmission (MUST).
In MUST communication in an LTE or LTE-A system, pairing between two or more user equipments is allowed. A base station transmits information to these user equipments on a same time-frequency resource, so that signals sent by the base station to the user equipments share a transmit power of the base station on the time-frequency resource. When two user equipments are paired with each other, powers at which the base station sends signals to the two user equipments may be different. Considering that compared with a far user equipment, a near user equipment is closer to the base station and has a better channel condition, to ensure that both the far and near user equipments can perform reliable transmission, the base station usually allocates a smaller downlink transmit power to the near user equipment, and allocates a larger downlink transmit power to the far user equipment.
Because a total transmit power of the far user equipment and the near user equipment of the base station is determined, the base station needs to determine a downlink transmit power ratio of the near user equipment to the far user equipment before sending downlink signals.